The present invention relates to a method of discriminating a sample for a sensor system which measures the concentration of a target substance (substance of interest) contained in the sample, in particular for a biosensor system which quantitates the concentration of glucose, cholesterol or the like contained in a body fluid such as blood by measuring electric current. More particularly, it relates to a sample discriminating method of automatically discriminating whether the sample introduced to a sensor system is a body fluid or a standard fluid, the sensor system being designed to periodically examine whether the accuracy of the sensor system is maintained or not, using the standard fluid, whose concentration has been known, instead of the body fluid.
There has been well known a sensor system which quantitates the concentration of a target substance contained in a sample by measuring electric current. In recent years, the sensor system described above has been widely applied to, for example, a biosensor system such as a small and easy type of blood sugar measuring system for quantitating the value of blood sugar contained in blood, or the like. Recently, the blood sugar measuring system, which is used for a blood sugar diagnosis or daily management of a diabetes patient, is commercially prevailed while being provided with many various functions. Recently, for example, the blood sugar measuring system is particularly of great importance in the field of a data management such as a management or processing of measured data.
In general, measurement accuracy of the biosensor system including a sensor and a measuring device is periodically managed using, for example, an exclusive standard fluid (referred to xe2x80x9ccontrol fluidxe2x80x9d hereinafter), in order to maintain or manage the measuring accuracy. As the control fluid, there may been used a solution in which a known amount of glucose is dissolved in pure water, the solution being colored with a pigment in accordance with its use, or being provided with a hydrophilic polymer so as to adjust its viscosity.
In the conventional biosensor system in which its measurement accuracy is managed using the control fluid, it is required that the measured data of the control fluid is not confusedly processed as the measured data of the body fluid or the like used as an ordinary sample. Accordingly, before the control fluid is introduced into the biosensor system, the measuring mode is changed to that for the control fluid by a predetermined manual operation of the measuring device so as to distinguish its measuring data from the measuring data of the body fluid or the like.
However, in the conventional biosensor system described above, when the control fluid is introduced, it is required to change the measuring mode by the manual operation for changing the mode, for example, button operation or the like. In consequence, there is such a problem that the measured data for the control fluid may be managed while erroneously being recognized as the measured data for the body fluid or the like by erroneously performing or forgetting the operation. Meanwhile, there may be also such a problem that the operation for manually changing the mode is troublesome. In particular, for a diabetes patient or the like having trouble in the eyes or fingertips, it may be difficult to change the mode by the manual operation. Therefore, there is requested a biosensor system, which can automatically discriminate whether a sample introduced into the biosensor system is a body fluid or a control fluid.
The present invention, which has been developed to solve the conventional problems described above, has an subject to provide a means which can automatically discriminate the kind of a sample for a sensor system that quantitates the concentration of a target substance contained in the sample by measuring electric current, for example, a biosensor system such as a blood sugar measuring system.
A sample discriminating method according to the present invention which has been developed to achieve the above-mentioned object, is a method of discriminating a sample for a sensor system which quantitates the concentration of a target substance (substance of interest) contained in the sample by measuring electric current, the method comprising the steps of, (i) using a ratio of a measured current value to a time-differential or time-difference value of the current value as a discriminating parameter, (ii) defining a discrimination function for discriminating kinds of a plurality of objective samples, the discrimination function using the discriminating parameter as an independent variable, (iii) using a numeric value obtained by substituting the value of the discriminating parameter into the discrimination function as a discriminating index, and (iv) automatically discriminating the kind of any sample based on the discriminating index.
As the discriminating function, for example, there may be given a discriminant function, a Mahalanobis distance or the like.
According to the sample discriminating method of the present invention, because the kind of the sample can be automatically discriminated, the kind of the sample may not be erroneously recognized due to erroneously performing or forgetting the operation. Further, because it is not necessary to change the mode by a manual operation, even a person having trouble in the eyes or fingertips can easily use the sensor system.
The discrimination function may be defined by means of an equation using only one discriminating parameter or independent variable. However, in order to raise the accuracy of the discrimination, it is more preferable that the discrimination function is defined by means of an expression using a plurality of, for example two, discriminating parameters or independent variables.
The discrimination function may be defined by means of a linear expression for the discriminating parameter. Meanwhile, the discrimination function may be defined by means of a expression of high degree, for example an expression of nth degree (n=2, 3, 4, . . . ), for the discriminating parameter.
The sample discriminating method according to the present invention is particularly effective for such a case that the kinds of the samples to be discriminated are a body fluid such as blood and a control fluid. In this case, it is preferable that the sensor system is automatically judged whether it is right or not, namely the system is checked, based on a quantitated value of the concentration of the target substance in the control fluid, and then a resultant judgement is indicated.
Meanwhile, in the sample discriminating method according to the present invention, it is preferable that when the value of the discriminating index is within such a predetermined range that it is difficult to discriminate the kind of the sample, namely it exists within a region near a boundary, the kind of the sample is not automatically discriminated while it is indicated that the discrimination has not been performed. If so, the accuracy or preciseness of the automatic discrimination of the kind of the sample may be highly improved.
Although it may be a rare case that the kind of the sample is not automatically discriminated so that it is indicated that the discrimination has not been performed, the kind of the sample may be designated by a manual operation in the above-mentioned case.